(N₂)³⁻ Radical Chemistry via Trivalent Lanthanide Salt/Alkali Metal Reduction of Dinitrogen: New Syntheses and Examples of (N₂)²⁻ and (N₂)³⁻ Complexes and Density Functional Theory Comparisons of Closed Shell Sc³⁺, Y<sup>3

New syntheses of complexes containing the recently discovered (N2)3− radical trianion have been developed by examining variations on the LnA3/M reductive system that delivers “LnA2” reactivity when Ln = scandium, yttrium, or a lanthanide, M = an alkali metal, and A = N(SiMe3)2 and C5R5. The first examples of LnA3/M reduction of dinitrogen with aryloxide ligands (A = OC6R5) are reported: the combination of Dy(OAr)3 (OAr = OC6H3tBu2-2,6) with KC8 under dinitrogen was found to produce both (N2)2− and (N2)3− products, [(ArO)2Dy(THF)2]2(μ-η2:η2-N2), 1, and [(ArO)2Dy(THF)]2(μ-η2:η2-N2)[K(THF)6], 2a, respectively. The range of metals that form (N2)3− complexes with [N(SiMe3)2]− ancillary ligands has been expanded from Y to Lu, Er, and La. Ln[N(SiMe3)2]3/M reactions with M = Na as well as KC8 are reported. Reduction of the isolated (N2)2− complex {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-N2), 3, with KC8 forms the (N2)3− complex, {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-N2)[K(THF)6], 4a, in high yield. The reverse transformation, the conversion of 4a to 3 can be accomplished cleanly with elemental Hg. The crown ether derivative {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-N2)[K(18-crown-6)(THF)2] was isolated from reduction of 3 with KC8 in the presence of 18-crown-6 and found to be much less soluble in tetrahydrofuran (THF) than the [K(THF)6]+ salt, which facilitates its separation from 3. Evidence for ligand metalation in the Y[N(SiMe3)2]3/KC8 reaction was obtained through the crystal structure of the metallacyclic complex {[(Me3Si)2N]2Y[CH2Si(Me2)NSiMe3]}[K(18-crown-6)(THF)(toluene)]. Density functional theory previously used only with reduced dinitrogen complexes of closed shell Sc3+ and Y3+ was extended to Lu3+ as well as to open shell 4f9 Dy3+ complexes to allow the first comparison of bonding between these four metals.